Recently, a secondary battery, which can be charged and discharged, has been widely used as an energy source for wireless mobile devices. In addition, the secondary battery has attracted considerable attention as a power source for electric vehicles (EV) and hybrid electric vehicles (HEV), which have been developed to solve problems, such as air pollution, caused by existing gasoline and diesel vehicles using fossil fuels.
Small-sized mobile devices use one or several battery cells for each device. On the other hand, middle or large-sized devices, such as vehicles, use a middle or large-sized battery pack having a plurality of battery cells electrically connected to one another because high output and large capacity are necessary for the middle or large-sized devices.
Preferably, the middle or large-sized battery pack is manufactured so as to have as small a size and weight as possible. For this reason, a prismatic battery or a pouch-shaped battery, which can be stacked with high integration and has a small weight to capacity ratio, is usually used as a battery cell of the middle or large-sized battery pack. In particular, much interest is currently focused on the pouch-shaped battery, which uses an aluminum laminate sheet as a sheathing member, because the pouch-shaped battery is lightweight, the manufacturing cost of the pouch-shaped battery is low, and it is easy to modify the shape of the pouch-shaped battery.
In order for the middle or large-sized battery pack to provide output and capacity required by a specific apparatus or device, it is necessary for the middle or large-sized battery pack to be configured to have a structure in which a plurality of battery cells is electrically connected in series to each other or in series and parallel to each other and the battery cells are stable against external force.
Specifically, when the battery cells are connected in parallel to each other, electrode terminals of the respective battery cells are connected to each other by one to one welding at a single weld point.
When three or more battery cells are connected in parallel to one another while being stacked, however, three or more connections between the electrode terminals of the battery cells are needed with the result that the structure of the battery pack becomes complicated and internal resistance increases when the same region is welded.
Meanwhile, a conventional battery pack is generally manufactured by fixing battery modules to a base plate and using an end plate and a support bar for a portion of battery modules in order to secure dynamic stability.
However, the battery pack having the above structure has spatial limitations in mounting the battery modules therein. In a case in which a large number of battery modules are used to constitute the battery pack, the structural stability of the battery pack is lowered.
In addition, the conventional battery pack is configured to have a structure in which the battery modules are fixed to the base plate using bolts or nuts such that the battery modules cannot be moved upward and downward and the battery modules are fixed in the longitudinal direction using the end plate and the support bar in order to secure dynamic stability.
In the battery pack having the above structure, however, the battery modules are fixed to the base plate using fastening members, such as a plurality of bolts or nuts with the result that an assembly process is complicated and troublesome. In addition, it is necessary to secure a space for the fastening members, resulting in spatial limitations and weight limitations of the fastening members.
Furthermore, for secondary batteries, such as pouch-shaped batteries, each of which has an electrode assembly mounted therein, a plurality of battery cells is mounted in a cell cover. However, insulation of the secondary batteries is destroyed due to contact between sealed portions of the battery cells and the cell cover with the result that safety of the secondary batteries is lowered.
Therefore, there is a high necessity for a battery pack having a compact structure securing safety that is capable of solving the above problems.